(NBC News) – A single bald eagle found dead in southern Delaware last Saturday didn't raise red flags for state wildlife officials.

But then a few hours later and a mile away, a startling scene unfolded: Eight bald eagles — distressed and disoriented — were discovered on the ground, barely moving on a fallow farm field.

"Seeing one in a field wouldn't be irregular, but then so many of them — and they weren't sitting up," said Sgt. John McDerby of Delaware's Fish and Wildlife Natural Resources Police. "It was a devastating sight."

Three of the eagles died, two were rescued and the rest flew away, officials said. The following day, another dead bird was found during a sweep.

The cluster of deaths comes just a month after 13 bald eagles died about 35 miles away on the Eastern Shore of Maryland — the largest single die-off of bald eagles in the state in three decades.

This mystery surrounding the bird species that has soared back from the brink of extinction has investigators and wildlife advocates asking: Is someone poisoning or intentionally harming these national symbols?

At this point, investigators can't say, but they aren't ruling out a criminal act.

In Maryland, necropsies indicated the birds did not die from natural causes, meaning diseases such as avian influenza can be ruled out. But they did not pinpoint a cause of death. [more]